My next aquisition will be a SBS, based on a Remington 870. My question pertains to papering. Most threads I have located indicate that the shotgun (receiver) becomes the papered item. If I add a serial number to the barrel, can I paper just that? This would keep the actual receiver from becoming a restricted item and the barrel would be easier to transfer if I ever got rid of it.
No, you register the firearm. I believe you can mark the barrel with your name and state to meet the requirements of a Form 1 (I know you can with an SBR), but even then it’s still the firearm (receiver) that is the NFA item.
There are unique exceptions that may lead you to this line of thought, such as a drop-in auto sear being the registered part of some machineguns, but for an SBS it’s the receiver, not the short barrel, that must be registered.